1. The Field of Invention
The present invention relates to an airbag module housing. More specifically, the present invention relates to maintaining a Z-height between two members of an airbag module.
2. The Relevant Technology
In the modern day automobile, the airbag has become as important an automobile safety feature as the seatbelt. Government standards and consumer demands have dramatically increased airbag use throughout the automobile. Airbag deployment occurs when sensors detect an abnormal deceleration in the automobile, triggering an explosive charge that immediately inflates the airbag. The airbag deploys into the automobile cabin, dampening the occupants"" acceleration toward any rigid interior components and preventing serious injury or death. The success of airbags has caused automobile manufactures to install airbags in multiple locations throughout the automobile cabin, including the steering wheel, the passenger side dashboard, and the side doors. However, due to size restrictions of these locations, designers must often balance maximum safety with minimum size.
Airbag modules require accurate and consistent placement of each member of the module. Many airbag designs implement similar module members, such as airbags, airbag covers, and reaction housings. A reaction housing and an airbag cover typically mate or interlock to form an airbag storage volume. The airbag storage volume is defined as the volume between the interlocked reaction housing and airbag cover. The airbag is placed in a folded state within the airbag storage volume. The airbag will generally have an inflation opening where the airbag attaches to the reaction housing and the airbag is then positioned within the reaction housing to deploy toward the airbag cover. The airbag cover typically has a front panel that is exposed to the automobile cabin and a skirt that extends from the back surface of the front panel. The skirt provides an opening to mate the reaction housing to the airbag cover. The airbag cover is designed to release the airbag into the automobile cabin upon inflation of the airbag. Airbag covers release airbags from the storage volume and into the passenger compartment by using hinged or pivotal doors to release the airbag or by tear-lines in the front panel of the cover that tear apart when the airbag deploys.
To facilitate deployment of an airbag through the airbag cover and into the automobile cabin, airbag modules typically use the different relative strengths between the reaction housings and the airbag cover. Because the pivotal door or the tear lines in the airbag cover are designed to yield when an airbag deploys, the relative strength of the airbag cover must be smaller than the strength of the reaction housing. Consequently when an airbag expands, the reaction housing acts as a reaction surface from which the expanding airbag may exert an equal and opposite load on the airbag cover. The airbag cover yields to the expanding airbag, allowing the inflated airbag to deploy away from the reaction housing and into the automobile cabin.
Airbag module designs require consistent placement of each module member within the airbag module to maintain a proper airbag storage volume. As previously discussed, the storage volume is defined as the region between the interlocked airbag cover and reaction housing. The critical measurement in the airbag storage volume is the Z-height. The Z-height is the distance between the back surface of the airbag cover and the reaction surface of the reaction housing. The Z-height changes as the reaction housing and the airbag cover move relative to each other. Thus, as the two members are pulled apart, the Z-height increases and as the two members are compressed together, the Z-height decreases. Significant displacement of the defined Z-height can interfere with proper airbag operation. For example, because airbag covers are typically an aesthetic member of the automobile cabin, an incorrect Z-height will prevent the cover from sitting flush with the other interior components. Also, airbag covers on steering wheels are typically connected with the horn. If the Z-height is displaced, it may cause the horn to constantly actuate or to not operate at all. In extreme situations, an improper Z-height displacement can interfere with the deployment of the airbag. This may cause the airbag to deploy incorrectly. Additionally, if a Z-height displacement compromises the coupling between the reaction housing and the airbag cover, a deploying airbag may project the airbag cover toward the automobile passenger.
To maintain a functional Z-height, a mode of fastening the airbag cover to the reaction housing must be carefully selected. The fastener mode should be low cost and easy to assemble. More importantly the fastener mode must maintain a proper Z-height when the reaction housing and airbag cover receive compressive and tensile loads. If an inadequate fastener mode is selected, the coupling between airbag cover and reaction housing may fail, causing the airbag to malfunction. A common type of fastening mode used in airbag modules is an integrally formed fastener. Integrally formed fasteners are manufactured as a part of the module member to which it is associated. Examples of integrally formed fasteners may include snap fits, slot and latches, and hook and windows. These fastener designs are less expensive than traditional fasteners, such as screws, and require significantly less assembly time.
An exemplary embodiment of an interference fastener for an airbag module is the hook and widow design. Hook and widow fasteners are inexpensive to manufacture and are easy to assemble. They are also capable of a wide variety of embodiments. Hook and window fasteners typically comprise a protruding xe2x80x9cJxe2x80x9d shaped hook on a first mating member and a cutout window on a second mating member. The xe2x80x9cJxe2x80x9d shaped hook slides through the window and engages an edge of the window with the curved section of the hook. Any tensile load applied to the hook will only serve to anchor the hook further to the window. This fit is ideal for withstanding the large tensile loads induced by an airbag exploding between the reaction housing and the airbag cover.
Unfortunately, a simple hook is not adequate for withstanding compressive loads between the reaction housing and the airbag cover. Compressive loads work against the hook and window design by disengaging the hook from the window""s edge. Consequently, designers have added various geometries to the hook to allow for proper maintenance of the Z-height during both tensile and compressive loads. Secondary processes, such as crimping the hooks, have been used to create geometries that can properly maintain the Z-height. These geometries engage other parts of the window or airbag module to maintain the Z-height during compressive loads. However, these secondary processes can add cost to the manufacturing process of an airbag module.
Single shot injection molding processes have been used to create hook geometries that can maintain the Z-height during both tensile and compressive loads while using a single step manufacturing process. Various designs of hook and window fasteners can be manufactured with an injection molding process because of the ability in molding to control the shape of the fastener in three dimensions. The three-dimensional nature of injection molding allows designers to add steps or shelves to a hook that will prevent compression of the Z-height and reduction of the airbag storage volume. Further, the injection molding process may use plastics or metals in the airbag module and fastener designs. The flexibility of injection molding makes it a widely used process in manufacturing airbag modules. However, despite all the discussed advantage of injection molding, molding does not necessarily produce the strongest and least expensive airbag module components.
Manufacturers seeking to produce the highest strength airbag modules at the lowest cost have turned to metal stamping processes to form some of the airbag module components. Stamping involves placing a generally thin sheet of metal over a form and then stamping the sheet into the form, forcing the sheet into the shape of the form. Stamping can create various holes and lips in the sheet of metal in a single-step process. Stamped airbag components provide the high strength and ductility of metal with the cost effectiveness of a single-step manufacturing process. Further, the equipment required for stamping is less expensive than the equipment required for injection molding.
One drawback with current stamping processes in airbag module design is the limitation of only being able to form objects in two dimensions. The single motion stamping process has been unable, thus far, to produce a three-dimensional geometry hook or other adequate structure that can maintain an airbag module Z-height during tensile and compressive loads without secondary manufacturing processes. An airbag module design capable of maintaining a proper Z-height during tensile and compressive loads while also capable of being manufactured by a single-step, stamped metal process would provide superior strength, cost, and operational advantages over similar injection molded or multi-stepped airbag module designs.
Accordingly, a need exists for an airbag module that is capable of substantially maintaining the Z-height of an airbag placement volume in tensile and compressive loads that can also be manufactured by a single-step metal stamping process.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available airbag module designs. Thus, it is an overall objective of the present invention to provide an airbag module that is capable of substantially maintaining the Z-height of an airbag placement volume in tensile and compressive loads that can also be manufactured by a single-step metal stamping process.
To achieve the foregoing objective, and in accordance with the invention as embodied and broadly described herein in the preferred embodiment, an airbag module with a Z-height control tab is provided. According to one configuration, the airbag module may comprise a reaction housing and an airbag cover. The reaction housing further comprises a plurality of mounting projections and the airbag cover comprises a skirt with a plurality of windows corresponding to the mounting projections. The reaction housing and the cover interlock via the mounting projections and the skirt windows to define a Z-height, the internal distance between the reaction housing and the airbag cover. The Z-height is substantially maintained during tensile loads by the mounting projections and the Z-height is substantially maintained during compressive loads by the Z-height control tabs. The mounting projections prevent the Z-height from increasing and the Z-height control tabs prevent the Z-height from decreasing.
In a preferred embodiment the reaction housing is manufactured by a single-step, metal stamping process. The Z-height control tabs are created in a shoulder section of the reaction housing as the housing is stamped into shape, thus integrally forming the tabs into the reaction housing. The Z-height control tabs may also extend from the shoulder portion of the reaction housing at any number of angles, such that the Z-height control tabs engage the top of the skirt in a net to interference fit. This provides a secure fit between the reaction housing and the airbag cover. Alternatively, the Z-height control tabs may be semi-deflectable to facilitate an interference fit with the skirt.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.